Exhaust gas purifying apparatus

ABSTRACT

In a hybrid vehicle equipped with an exhaust gas purifying apparatus, when a gasoline engine stops, an exhaust gas passage is closed by a pair of upstream-side and downstream-side throttle units to form an accommodation space. A pressure reduction unit reduces a pressure of the closed accommodation space where a three way catalyst is placed. The exhaust gas around the three way catalyst in the closed accommodation space does not leak into either an outside atmosphere side or into the gasoline engine side. Reducing the pressure in the closed accommodation space decreases heat conduction through the exhaust gas toward the outside. It is thereby possible to prevent the temperature drop of the three way catalyst and to keep the three way catalyst at a temperature of not less than its activation temperature for a long period of time even if the gasoline engine stops.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese Patent Application No. 2008-8306 fled on Jan. 17, 2008, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas purifying apparatus to be mounted to a hybrid vehicle using two or more distinct power sources such as an electric motor and an internal combustion engine, and in particular, relates to the exhaust gas purifying apparatus capable of purifying specified materials such as hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in an exhaust gas emitted from the internal combustion engine.

2. Description of the Related Art

For internal combustion engines such as diesel engines and gasoline engines, reduction of specified materials has been proposed. The specified materials are hydro carbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), and others contained in an exhaust gas emitted from an internal combustion engine of a hybrid vehicle. In general, a hybrid vehicle as well as another vehicle using a fuel source is equipped with an exhaust gas purifying apparatus with catalyst The catalyst is capable of capturing and eliminating such specified material contained in an exhaust gas emitted from the internal combustion engine. A catalyst unit is filled with catalyst and is placed in an exhaust gas passage in the exhaust gas purifying apparatus.

The catalyst must be used at an adequate temperature not less than its activation temperature in order to keep its function to capture and eliminate the specified materials from the exhaust gas.

By the way, the temperature of the exhaust gas emitted from the internal combustion engine is decreased, namely, becomes low when the power source in the hybrid vehicle is switched to the electric motor and the internal combustion engine is halted in operation. Because the catalyst is heated by the heat energy of the exhaust gas, the temperature of the catalyst is also decreased when the internal combustion engine stops.

In order to solve the above problem, there have been proposed conventional techniques. For example, Japanese patent laid open publication NO. H05-195748 has disclosed a technique to close an exhaust gas passage at the downstream side of a catalyst unit in the direction of an exhaust gas flow in order to limit the stream of the exhaust gas from the exhaust gas passage to the outside of the exhaust gas purifying apparatus, namely, to the outside atmosphere. This maintains the temperature of the catalyst at its activation temperature.

However, according to recent technical advances, the internal combustion engine in the hybrid vehicle is temporarily halted even if the hybrid vehicle is running. At that time, the heat energy of the exhaust gas is discharged to not only the downstream side of the exhaust gas passage but also the upstream side in the internal combustion engine side. This causes insufficient heat insulation, and as a result, the temperature of the catalyst becomes low. In particular because the hybrid vehicle repeats operation and stop of the internal combustion engine while the hybrid vehicle is running, the exhaust gas is intermittently supplied to the catalyst in the catalyst unit. This causes the temperature drop of the catalyst. As a result, it is impossible to maintain the catalyst at its activation temperature for a long period of time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exhaust gas purifying apparatus having a structure to prevent heat transfer from a catalyst placed therein toward an internal combustion engine side as well as outside atmosphere side, and capable of keeping the catalyst at its activation temperature for a long period of time.

To achieve the above purposes, the present invention provides an exhaust gas purifying apparatus to be mounted onto a hybrid vehicle and others. The hybrid vehicle is equipped with an internal combustion engine and an electric motor as power sources. The exhaust gas purifying apparatus is capable of capturing and purifying specified materials such as hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in an exhaust gas emitted from the internal combustion engine. The exhaust gas purifying apparatus has an exhaust gas pipe, a catalyst unit with catalyst, and a pair of an upstream-side throttle unit and a downstream-side throttle unit. The upstream-side throttle unit is placed at the upstream side in the exhaust gas pipe, namely at the internal combustion engine side, observed from the catalyst unit side. The downstream-side throttle unit is placed at the downstream side in the exhaust gas pipe, namely at the outside atmosphere side, observed from the catalyst unit side. The exhaust gas pipe forms an exhaust gas passage through which an exhaust gas emitted from the internal combustion engine flows. The catalyst unit with catalyst is placed in the exhaust gas passage. The upstream-side throttle unit and the downstream-side throttle unit are placed at the upstream side and the downstream side through the catalyst unit along the exhaust gas passage, respectively. Those throttle units are capable of opening and closing the exhaust gas passage.

The upstream-side throttle unit is placed at the upstream side, observed from the catalyst unit, in the exhaust gas passage, along the exhaust gas flow. The downstream-side throttle unit is placed at the downstream side, observed from the catalyst unit, in the exhaust gas passage, along the exhaust gas flow. Accordingly, the exhaust gas passage at the upstream side observed from the catalyst unit is opened and closed by the upstream side throttle unit. Completely closing the exhaust gas passage by the upstream-side throttle unit and the downstream-side throttle unit prevents the exhaust gas from leaking either toward the outside atmosphere side, namely, toward the downstream side of the catalyst, or toward the internal combustion engine side. As a result, the heat energy of the catalyst in the catalyst unit is not discharged toward the internal combustion engine side through the exhaust gas, nor toward the outside atmosphere side. It is therefore possible to keep the catalyst in the catalyst unit at a temperature of not less than its activation temperature for a long period of time even if the internal combustion engine stops.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross section of a part of an exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 2 is a schematic diagram of a hybrid vehicle equipped with the exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 3 is a flow chart showing the operation of the exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 4 is a diagram showing a relationship between an elapsed period of time counted from a gasoline engine stop and a temperature of a three way catalyst;

FIG. 5 is a diagram showing a relationship between a concentration of HC contained in an exhaust gas emitted from the gasoline engine and the elapsed period of time counted from the re-start of the gasoline engine;

FIG. 6 is a diagram showing a relationship between the temperature of the three way catalyst and the elapsed period of time counted from the gasoline engine stop just after a high speed running of the hybrid vehicle;

FIG. 7 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the second embodiment of the present invention; and

FIG. 8 is a schematic cross section of a part of an exhaust gas purifying apparatus according to the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.

A description will be given of the exhaust gas purifying apparatus mounted to a hybrid system in a hybrid vehicle according to first to third embodiment with reference to FIG. 1 to FIG. 8. Through the first to third embodiments, the same components will be referred with same reference characters and numbers.

First Embodiment

FIG. 2 is a schematic diagram of the hybrid system 10 in a hybrid vehicle equipped with the exhaust gas purifying apparatus 13 according to the first embodiment of the present invention.

The hybrid system 10 is equipped with and the exhaust gas purifying apparatus 13 and a pair of distinct power sources such as an engine system 11 (as an internal combustion engine system) and an electric motor 12.

The engine system 11 comprises a gasoline engine 14, an exhaust gas system 15, and a control unit 16. The engine system 11 further comprises an intake air system (not shown) and a gasoline supply system (not shown), and other components. The gasoline engine 14 has a plurality of cylinders 17. An injector 18 is mounted to each cylinder 17. The injector 18 injects gasoline as fuel into the corresponding cylinder 17. The hybrid system 10 equipped with the exhaust gas purifying apparatus according to the embodiments of the present invention. The engine system 11 has the gasoline engine as one power source which uses gasoline as fuel. For example, it is also possible for this engine system 11 to use liquefied petroleum gas (LPG), liquefied natural gas (LNG), or alcohols, instead of such a gasoline. Still further, it is possible for the engine system 11 to have a diesel engine instead of the gasoline engine 14.

As shown in FIG. 2, the exhaust gas system 15 has an exhaust gas pipe 22 that forms an exhaust gas passage 21. One end part of the exhaust gas pipe 22 communicates with each of the cylinder 17 in the gasoline engine 14. The other end part of the exhaust gas pipe 22 is released to outside atmosphere.

The control unit 16 is an electronic control unit (ECU) that is capable of controlling the entire of the hybrid system 10 comprised of the engine system 11, the electric motor 12, and the exhaust gas purifying apparatus 13.

The control unit 16 is a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and others, which are omitted from FIG. 2. The control unit 16 communicates with other control units for the hybrid system 10 in the hybrid vehicle through a vehicle local area network (or a vehicle LAN for short, not shown).

The control unit 16 controls the amount of gasoline to be injected by the injector 18 based on an amount of the accelerator pedal of the vehicle. The control unit 16 further controls the amount of electric power to be transmitted from a battery to the electric motor 12.

The electric motor 12 is an alternative current (AC) motor such as an induction motor. The control unit 16 controls the operation of the gasoline engine 14 and the electric motor 12, namely, switches the gasoline engine 14 and the electric motor 12 based on the charged amount of electric power in the battery and the drive condition of the hybrid vehicle. In particular, the electric motor acts as an electric power generator when the hybrid vehicle brakes. Thus, the driving energy of the hybrid vehicle is regenerated as a regeneration electric power when the hybrid vehicle brakes. This charged electric energy is charged into the battery. The battery is a secondary battery such as a lithium battery.

The exhaust gas purifying apparatus 13 comprises a three way catalyst 24, a temperature sensor 25, an upstream-side throttle unit 30, a downstream-side throttle unit 40, and a pressure reducing unit 50 (acting as a pressure reducing means), in addition to the control unit 16 in the hybrid system 10, and the exhaust gas pipe 22 in the engine system 11. In particular, the three way catalyst 24, the temperature sensor 25, the upstream-side throttle unit 30, the downstream-side throttle unit 40, and the pressure reducing unit 50 are placed in the exhaust gas system 15 of the engine system 11.

When the temperature of the three way catalyst 24 reaches its activation temperature, the three way catalyst 24 oxidizes hydro carbon (HC) contained in the exhaust gas into water (H₂O) and carbon dioxide (CO). Further, the three way catalyst 24 in the catalyst unit oxidizes carbon monoxide (CO) contained in the exhaust gas into carbon dioxide (CO₂). Still further, the three way catalyst 24 in the catalyst unit reduces nitrogen oxide (NOx) contained in the exhaust gas into nitrogen (N₂).

Although the first embodiment uses such a three way catalyst, it is possible to use another type of catalyst such as ammonia oxidizing catalyst, NOx selective reduction catalyst, or NOx adsorbing catalyst.

The temperature sensor 25 is placed in the exhaust gas pipe 22. The temperature sensor 25 is composed mainly of a temperature detection element such as a thermistor. The temperature sensor 25 detects the temperature of the exhaust gas flowing in the exhaust gas passage 21, and generates and transfers a detection signal corresponding to the detected temperature of the exhaust gas into the control unit 16. When receiving the detection signal transferred from the temperature sensor 25, the control unit 16 obtains the temperature of the exhaust gas. The control unit 16 indirectly estimates the temperature of the three way catalyst 24 based on the detected temperature of the exhaust gas.

The present invention is not limited by the first embodiment described above to indirectly estimate the temperature of the three way catalyst 24 based on the temperature of the exhaust gas flowing in the exhaust gas passage 21. It is possible to use another detection method, for example, which directly detects the temperature of the three way catalyst 24 using the temperature sensor 25 placed in the catalyst unit with the three way catalyst. It is also possible to estimate the temperature of the three way catalyst 24 based on the temperature of a cooling water for the gasoline engine 14 of the engine system 11 or the injection amount of fuel by the injector 18.

FIG. 1 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the first embodiment of the present invention.

The catalyst unit with the three way catalyst 24 is placed in the exhaust gas passage 21 in the exhaust gas pipe 22.

The upstream-side throttle unit 30 is placed at the upstream side of the three way catalyst 24, namely, at the gasoline engine 14 side observed from the catalyst unit with the three way catalyst 24 along the exhaust gas flow in the exhaust gas passage 21.

As shown in FIG. 1, the upstream-side throttle unit 30 has a throttle valve member 31 and a valve drive unit 32.

The throttle valve member 31 opens and closes the exhaust gas passage 21. When receiving a control signal transferred from the control unit 16, the valve drive unit 32 drives the throttle valve member 31 to rotate around a rotary shaft 33. The valve drive unit 32 drives the throttle valve member 31 to rotate from a fully opened state to a fully closed state.

In the fully opened state, the valve drive unit 32 is in parallel to the exhaust gas flow in the exhaust gas passage 21. In the fully closed state, the valve drive unit 32 is perpendicular in position to the exhaust gas flow in the exhaust gas passage 21. The diameter of the throttle valve member 31 is approximately equal to the inner diameter of the exhaust gas pipe 22. Therefore when the throttle valve member 31 is in the fully closed state, the throttle valve member 31 completely closes the exhaust gas passage at the upstream side of the catalyst unit with the three way catalyst 24.

On the other hand, the downstream-side throttle unit 40 is placed in the exhaust gas passage 21 at the downstream side of the three way catalyst 24, namely, in the opposite position of the gasoline engine 14 side observed from the catalyst unit with the three way catalyst 24 along the exhaust gas flow in the exhaust gas passage 21.

The downstream-side throttle unit 40 has a throttle valve member 41 and a valve drive unit 42. The throttle valve member 41 opens and closes the exhaust gas passage 21. When receiving a control signal transferred from the control unit 16, the valve drive unit 42 drives the throttle valve member 41 to rotate around a rotary shaft 43. The valve drive unit 42 drives the throttle valve member 41 to switch between the fully opened state and the fully closed state.

In the fully opened state, the valve drive unit 42 is in parallel to the exhaust gas flow in the exhaust gas passage 21. In the fully closed state, the valve drive unit 42 is perpendicular to the exhaust gas flow in the exhaust gas passage 21. The diameter of the throttle valve member 41 is approximately equal to the inner diameter of the exhaust gas pipe 22. Therefore when the throttle valve member 41 is in the fully closed state, the throttle valve member 41 completely closes the downstream side of the three way catalyst 24.

The pressure reducing unit 50 has a pressure reducing pump 51 and a pressure reducing passage 52. Through the pressure reducing passage 52, the downstream-side throttle unit 40 which is placed at the downstream side of the three way catalyst 24 communicates with the outside atmosphere. The pressure reducing pump 51 is placed in the middle of the pressure reducing passage 52. The pressure reducing pump 51 is driven based on the drive signal transferred from the control unit 16. The pressure reducing pump 51 sucks the exhaust gas in the exhaust gas passage 21 at the downstream side of the three way catalyst 24 closed by the downstream-side throttle unit 40, and discharges the sucked exhaust gas into the outside atmosphere.

When the control unit 16 instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to enter the fully closed state, an accommodation space 26 is formed in the exhaust gas passage 21 in which the catalyst unit with the three way catalyst 24 is placed. Thus, the accommodation space 26 is formed between the upstream-side throttle unit 30 and the downstream-side throttle unit 40. At that time, the control unit 16 instructs the pressure reducing pump 51 to discharge the exhaust gas from the accommodation space 26 to the outside atmosphere, so that this reduces the pressure in the accommodation space 26 which is formed between the upstream-side throttle unit 30 and the downstream-side throttle unit 40 in the exhaust gas passage 21.

Next, a description will now be given of the operation flow of the exhaust gas purifying apparatus 13 according to the first embodiment with reference to FIG. 3.

FIG. 3 is a flow chart showing the operation of the exhaust gas purifying apparatus 13 according to the first embodiment of the present invention.

The control unit 16 judges whether or not the engine system 11 is now operating (step S101). When the judgment result in step S101 indicates that the engine system 11 is now operating, the control unit 16 completes this routine shown in FIG. 3.

In the case of the hybrid vehicle equipped with the gasoline engine 14 of the engine system 11 and the electric motor 12, the control unit 16 switches the gasoline engine 14 and the electric motor 12 according to the charged condition of the battery 23. In other words, the control unit 16 controls the engine system 11 to intermittently repeat drive and stop of the gasoline engine 14 according to the driving condition of the hybrid vehicle and the charged condition of the battery 23.

The three way catalyst 24 in the exhaust gas purifying apparatus 13 is heated by the exhaust gas which is emitted from the engine system 11 when the gasoline engine 14 as the internal combustion engine is operating. Therefore it is not necessary to warm the three way catalyst 24 during the operation of the gasoline engine 14 because the exhaust gas warms the three way catalyst 24.

On the other hand, when the control unit 16 instructs the engine system 11 to stop the operation of the gasoline engine 14, and the gasoline engine 14 thereby stops its operation, no exhaust gas is supplied into the three way catalyst 24 through the exhaust gas passage 21. The temperature of the three way catalyst 24 is then decreased to be below its activation temperature. In order to avoid this, when detecting the stop of the gasoline engine 14, the control unit 16 instructs the components of the exhaust gas purifying apparatus 13 to warm the three way catalyst 24 in order to keep the temperature of the three way catalyst 24 at not less than the activation temperature of the three way catalyst 24.

When judging that the gasoline engine 14 of the engine system 11 does not operate in step S101, the operation flow goes to step S102. In step S102, the control unit 16 judges whether or not the temperature of the three way catalyst 24 is equal to not less than a predetermined temperature. For example, when the hybrid vehicle equipped with the hybrid system 10 stops its operation, the temperature of the three way catalyst 24 becomes almost equal to the temperature of the outside atmosphere. Thus, when the hybrid vehicle stops its operation, it is not necessary to warm the three way catalyst 24. In that case, the control unit 16 further judges whether or not remaining heat (heat left) is left to the gasoline engine 14. That is, the control unit 16 judges whether or not the temperature of the three way catalyst 24 is not less than the predetermined temperature which is more than the temperature of the outside atmosphere. In that case, it is possible to use a constant value as the predetermined temperature which is determined regardless of the temperature of the outside atmosphere.

When the judgment result indicates that the temperature of the three way catalyst 24 is less than the predetermined temperature, the control unit 16 completes the routine shown in FIG. 3.

When the judgment result in step S102 indicates that the temperature of the three way catalyst 24 is not less than the predetermined temperature, the control unit 16 instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to completely close the accommodation space 26 in the exhaust gas passage 21 (step S103). The control unit 16 transfers the drive signal to the valve drive unit 32 to fully close the throttle valve member 31. Further, the control unit 16 transfers the drive signal to the valve drive unit 42 to fully close the throttle valve member 41. This places the catalyst unit with the three way catalyst 24 in the closed accommodation space 26 formed between the throttle valve member 31 in the upstream-side throttle unit 30 and the throttle valve member 41 in the downstream-side throttle unit 40. That is, when detecting the operational stop of the gasoline engine 14, the control unit 16 instructs the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to completely close the accommodation space 26 in the exhaust gas passage 21 in which the three way catalyst 24 is placed.

When instructing the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to close the accommodation space 26, the control unit 16 then reduces the pressure of the accommodation space 26. When the accommodation space 26 is closed by the upstream-side throttle unit 30 and the downstream-side throttle unit 40, the control unit 16 instructs the pressure reducing pump 51 to start its operation. The pressure reducing pump 51 discharges the exhaust gas in the accommodation space 26 into the outside atmosphere through the pressure reducing passage 52. The pressure of the accommodation space 26 thereby drops. It is acceptable for the control unit 16 to drive the pressure reducing pump 51 until the gasoline engine 14 in the engine system 11 re-starts, or possible to stop the pressure reducing pump 51 when the pressure of the accommodation space 26 is decreased to a predetermined pressure.

In step S103, the control unit 16 completely closes the upstream-side throttle unit 30 and the downstream-side throttle unit 40 in order to completely close the accommodation space 26 in which the catalyst unit with the three way catalyst 24 is placed. This can prevent the exhaust gas remaining in the accommodation space 26 from leaking or being discharged to the gasoline engine 14 side and also to the outside atmosphere through the exhaust gas passage 21 at the downstream side of the catalyst unit. That is, this can prevent the leakage of heat energy of the three way catalyst 24 with the exhaust gas to leak or to be discharged toward both the upstream side and the downstream side of the three way catalyst 24. When compared with a conventional exhaust gas purifying apparatus as a comparison example without any upstream-side throttle unit 30 and downstream-side throttle unit 40, the structure of the exhaust gas purifying apparatus according to the present invention capable of closing the accommodation space 26 by both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 can prevent the temperature drop of the three way catalyst 24. As a result, the temperature of the three way catalyst 24 is maintained at its activation temperature for a long period of time even if the gasoline engine 14 stops.

In step S104, the control unit 16 instructs the pressure reducing unit 50 equipped with the pressure reducing pump 51 to reduce the pressure in the accommodation space 26, namely, to discharge the exhaust gas remained in the accommodation space 26. This can prevent the heat conduction and convection of the three way catalyst 24, and as a result, it is possible to prevent the temperature drop of the three way catalyst 24 in the catalyst unit. The heat energy of the accommodation space 26 and the catalyst unit in the exhaust gas pipe 22 is adequately larger than that of the exhaust gas remained in the accommodation space 26. Therefore even if the pressure in the accommodation space 26 is decreased, namely, even if the exhaust gas remained in the accommodation space 26 is discharged to the outside atmosphere, there is little the influence of the temperature drop of the three way catalyst 24. Thus, reducing the pressure in the accommodation space 26 can decrease the thermal conduction through the exhaust gas as the heating medium, and can maintain the temperature of the three way catalyst 24 for a long period of time even if the internal combustion engine stops its operation.

FIG. 4 is a diagram showing a relationship between the elapsed period of time counted from the gasoline engine 14 stop and the temperature of the three way catalyst 24.

That is, as clearly shown in FIG. 4, reducing the pressure in the accommodation space 26 after the gasoline engine 14 stops can prevent the temperature drop of the three way catalyst 24 rather than one example in which the accommodation space 26 is only closed and rather than a comparison example having no accommodation space 26 and not to reduce the pressure in the exhaust gas passage. Accordingly, the exhaust gas purifying apparatus having the above structure according to the first embodiment can keep the three way catalyst 24 at its activation temperature for a long period of time.

FIG. 5 is a diagram showing a relationship between a concentration of HC contained in the exhaust gas emitted from the gasoline engine 14 and the elapsed period of time counted from the re-starting time “A” of the gasoline engine 14.

The gasoline engine 14 is re-started at the timing “A” which is elapsed counted from the stop of the gasoline engine 14 shown in FIG. 4. FIG. 5 shows the change of the concentration of HC contained in the exhaust gas after the gasoline engine 14 restarts at the timing “A”.

In FIG. 5, the horizontal axis indicates the elapsed time counted from the timing “A” at which the gasoline engine 14 was re-started.

As described before, in the comparison example without having any upstream-side throttle unit 30 and the downstream-side throttle unit 40, the concentration of HC contained in the exhaust gas is drastically increased, as shown in FIG. 5. This means that the temperature of the three way catalyst 24 in the comparison example is much less than its activation temperature at the timing “A”. Therefore the exhaust gas containing a large amount of hydro carbon (HC) is discharged from the three way catalyst 24 until the temperature of the three way catalyst 24 reaches its activation temperature.

On the other hand, because the structure of the exhaust gas purifying apparatus according to the first embodiment closes the accommodation space 26 and further reduces the pressure in the accommodation space 26, the concentration of HC contained in the exhaust 25 gas from the catalyst unit with the three way catalyst 24 is decreased, after the gasoline engine 14 is re-starts at the timing “A”, as shown in FIG. 5. The reasons are as follows. As shown in FIG. 4, the temperature of the three way catalyst 24 at the timing “A” in the first embodiment is higher than that of the comparison example. Therefore even if the gasoline engine 14 re-starts at 30 the timing “A”, the structure of the exhaust gas purifying apparatus of the first embodiment can discharge the exhaust gas with less concentration of HC because the three way catalyst 24 can show its capacity to purify the specified materials such as HC, CO, and NOx contained in the exhaust gas.

After instructing the pressure reducing unit 50 to reduce the pressure in the accommodation space 26, in step S104, the control unit 16 judges whether or not the gasoline engine 14 re-starts its operation (step S105). The control unit 16 detects the re-start of the operation of the gasoline engine 14 based on the occurrence of the fuel injection from the injector 18, for example. When detecting the re-start of the gasoline engine 14, the control unit 16 instructs the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to fully open both the throttle valve member 31 and the throttle valve member 41 (step S106).

When the gasoline engine 14 is re-started, the engine system 11 discharges the exhaust gas. The three way catalyst 24 is heated again by the exhaust gas emitted from the gasoline engine 14.

The exhaust gas emitted from the gasoline engine 14 in the engine system 11 is discharged to the outside atmosphere through the exhaust gas passage 21. Fully opening both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 easily discharges the exhaust gas emitted from the gasoline engine 14 to the outside atmosphere without being disturbed. Accordingly, this can reduce the pressure loss of the exhaust gas flowing through the exhaust gas pipe 22.

As described above in detail, according to the exhaust gas purifying apparatus of the first embodiment, the control unit instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to close the exhaust gas passage 21 when the gasoline engine 11 stops its operation. This places the three way catalyst 24 into the closed accommodation space 26. Therefore the exhaust gas remaining around the three way catalyst 24 in the closed accommodation space 26 does not leak either to the outside atmosphere side or to the gasoline engine 14 side. As a result, because the heat conduction of the exhaust gas is decreased, it is possible to keep the three way catalyst 24 at the temperature of not less than its activation temperature for a long period of time. Still further, it is possible to decrease the concentration of hydro carbon (HC) contained in the exhaust gas when the gasoline engine 11 re-starts its operation.

Still further, according to the first embodiment of the present invention, the control unit 16 instructs the pressure reducing pump 51 to discharge the exhaust gas remained in the accommodation space 26 which is closed by the upstream-side throttle unit 30 and the downstream-side throttle unit 40. This decreases the amount of the exhaust gas remained in the closed accommodation space 26. Therefore decreasing the amount of the exhaust gas prevents the heat conduction and convection from the three way catalyst 24 placed in the closed accommodation space 26 toward both the outside atmosphere side and the gasoline engine 14 side.

Reducing the pressure of the closed accommodation space 26 prevents the exhaust gas from leaking out to the outside, where the exhaust gas has absorbed the heat energy of the three way catalyst 24 based on the difference in pressure between the closed accommodation space 26 and the outside. This decreases the heat conduction from the three way catalyst 24 and prevents the temperature drop of the three way catalyst 24. As a result, it is possible to keep the three way catalyst 24 at the temperature of not less than its activation temperature for a long period of time even if the gasoline engine 14 stops. Still further, it is possible to decrease the concentration of HC contained in the exhaust gas even if the gasoline engine 14 in the engine system 11 re-starts.

Still further, the control unit 16 instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to close the accommodation space 26, and instructs the pressure reducing unit 50 to reduce the pressure of the closed accommodation space 26. This control prevents the deterioration of the three way catalyst 24. For example, when the hybrid vehicle equipped with the exhaust gas purifying apparatus according to the first embodiment is running at a high speed, the control unit 16 selects using the gasoline engine 14 in the engine system 11 other than the electric motor 12 as the power source. This high-speed running increases the load of the gasoline engine 14 and also increases both the temperature of the exhaust gas and the temperature of the three way catalyst 24. When the gasoline engine 14 stops after such a high-speed running, the exhaust gas flow is halted while keeping the three way catalyst 24 at a high temperature. Further, the exhaust gas contains non-combustion HC. This non-combustion HC reacts with oxygen in the exhaust gas when the three way catalyst 24 is at a high temperature, like just following the high-speed running. Combusting HC in the three way catalyst 24 drastically increases the temperature of the three way catalyst 24. This causes the three way catalyst 24 deterioration.

FIG. 6 is a diagram showing a relationship between the temperature of the three way catalyst 24 and the elapsed period of time counted from the stop of the gasoline engine 11 just after a high-speed running of the hybrid vehicle.

In the structure of the exhaust gas purifying apparatus according to the first embodiment, because of discharging the exhaust gas which is remained in the closed accommodation space 26, namely, of reducing the pressure of the closed accommodation space 26, it is possible to decrease the concentration of oxygen remained in the closed accommodation space 26 where the catalyst unit with the three way catalyst 24 is placed.

As shown in FIG. 6, it is possible to suppress the temperature of the three way catalyst 24 from rising. Therefore it is possible to decrease the deterioration of the three way catalyst 24 caused by such HC combustion in the closed accommodation space 26.

Second Embodiment

A description will be given of the exhaust gas purifying apparatus according to the second embodiment of the present invention with reference to FIG. 7.

FIG. 7 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the second embodiment of the present invention. As shown in FIG. 7, the exhaust gas purifying apparatus of the second embodiment further comprises a heating unit 61 as a heating means. Instead, the exhaust gas purifying apparatus of the second embodiment does not have the pressure reducing unit 50 which is used in the structure of the first embodiment. The heating unit 61 is an electrical heater or a burner, where the electrical heater generates heat by electricity, and the burner generates heat by burning fuel.

The heating unit 61 is placed at the upstream side of the catalyst unit with the three way catalyst 24, namely, placed between the three way catalyst 24 and the upstream-side throttle unit 30.

The heating unit 61 generates heat energy only when the control unit 16 instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to close the exhaust gas passage 21, namely, to make the closed accommodation space 26 and to close the accommodation space 26.

The heating unit 61 heats both the closed accommodation space 26 and the three way catalyst 24 placed in the closed accommodation space 26.

When the temperature of the three way catalyst 24 is less than its activation temperature, the control unit 16 instructs the heating unit 61 to heat. It is thereby possible to keep the three way catalyst 24 at the temperature of not less than its activation temperature for a long period of time even if the gasoline engine 14 in the engine system 11 stops.

Because the exhaust gas purifying apparatus of the second embodiment is equipped with the heating unit 61 to heat the accommodation space 26 in the exhaust gas passage 21 closed by the upstream-side throttle unit 30 and the downstream-side throttle unit 40, it is possible to keep the three way catalyst 24 at its activation temperature or more. When using an electric heater as the heating unit 61, it is possible to use the electric power which is generated by the electric motor 12 while the hybrid vehicle brakes.

Third Embodiment

A description will be given of the exhaust gas purifying apparatus according to the third embodiment of the present invention with reference to FIG. 8.

FIG. 8 is a schematic cross section of a part of an exhaust gas purifying apparatus according to the third embodiment of the present invention. As shown in FIG. 8, the exhaust gas purifying apparatus of the third embodiment is equipped with a fuel injector 62 as a fuel addition means for the three way catalyst 24. On the other hand, the exhaust gas purifying apparatus of the third embodiment does not have the pressure reducing unit 50 which was used in the structure of the first embodiment.

The injector 62 has a function to inject gasoline as fuel, like the injector 18 for the gasoline engine 14 in the engine system 11. The injector 62 is placed at the upstream side of the catalyst unit, namely, placed between the catalyst unit with three way catalyst 24 and the upstream-side throttle unit 30.

When the control unit 16 instructs both the upstream-side throttle unit 30 and the downstream-side throttle unit 40 to close the accommodation space 26 in the exhaust gas passage 21, the control unit 16 instructs the injector 62 to inject the fuel into the exhaust gas passage 21, as shown in FIG. 8. Injecting the fuel by the injector 62 into the exhaust gas passage 21 in order to react the injected fuel with oxygen in the exhaust gas remaining in the exhaust gas passage 21, namely, to burn the fuel in the exhaust gas passage 21 by using remaining heat (or heat left) of the three way catalyst 24. As a result, burning the fuel heats the three way catalyst 24.

When the temperature of the three way catalyst 24 is less than the activation temperature and not less than a reaction acceptable temperature of the three way catalyst 24 during the operation of the hybrid system 10, the control unit 16 instructs the injector 62 to inject the fuel into the exhaust gas passage 21. This reaction acceptable temperature of the three way catalyst 24 is lower than the activation temperature, but within an acceptable temperature range to burn the injected fuel. For example, the activation temperature of the three way catalyst 24 is approximately 300° C. On the other hand, the reaction acceptable temperature of the three way catalyst 24 is approximately 100° C.

As described above, even if the temperature of the three way catalyst 24 is less than the activation temperature of the three way catalyst 24 after the gasoline engine 14 in the engine system 11 stops, the control unit 16 instructs the fuel injector 62 to inject the fuel into the exhaust gas passage 21 unless the temperature of the three way catalyst 24 is not less than the reaction acceptable temperature of the three way catalyst 24. It is thereby possible to heat the three way catalyst 24 by the combustion energy of the fuel, and to keep the three way catalyst 24 at the temperature of not less than the activation temperature for a long period of time.

In the structure of the third embodiment, the exhaust gas purifying apparatus is equipped with the fuel injector 62 to inject the fuel into the exhaust gas passage 21. The fuel injected by the fuel injector 62 is burned by remaining heat (heat left) of the three way catalyst 24, and the heat energy heats the three way catalyst 24. It is thereby possible to keep the three way catalyst 24 at the temperature of not less than the activation temperature.

It is also possible to combine the structures of the exhaust gas purifying apparatus according to the first to third embodiments of the present invention. For example, it is possible to add the pressure reducing unit 50 into the structure of each of the exhaust gas purifying apparatus according to the second and third embodiments of the present invention.

FEATURES AND EFFECTS OF THE PRESENT INVENTION

In the exhaust gas purifying apparatus as another aspect of the present invention, the throttle units completely close the exhaust gas passage in which the catalyst unit with the catalyst is placed. In the structure of the exhaust gas purifying apparatus, the upstream side of the catalyst and the downstream side of the catalyst in the exhaust gas passage are closed by the upstream-side throttle unit and the downstream-side throttle unit. Completely closing the exhaust gas passage by the upstream-side throttle unit and the downstream-side throttle unit prevents or limits the exhaust gas around the catalyst to leak into the internal combustion engine side at the upstream side of the catalyst and into the outside atmosphere side at the downstream side of the catalyst. It is thereby possible to keep the catalyst at a temperature of not less than its activation temperature for a long period of time even if the internal combustion engine stops.

The exhaust gas purifying apparatus as another aspect of the present invention further comprises a pressure reducing means capable of decreasing a pressure in the exhaust gas passage closed by the throttle units. This pressure reducing means reduces the pressure in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle unit. This can reduce the pressure in the exhaust gas passage in which the catalyst is placed between the upstream-side throttle unit and the downstream-side throttle unit. When compared with the pressure of the outside of the upstream-side throttle unit and the downstream-side throttle unit, the pressure in the exhaust gas passage around the catalyst is further decreased. As a result, it is possible to prevent the exhaust gas around the catalyst to flow, namely, to leak into the outside of the upstream-side throttle unit and the downstream-side throttle unit. This can keep the catalyst at the temperature of not less than its activation temperature. By reducing the pressure in the exhaust gas passage around the catalyst prevents the heat conduction through air. Accordingly, it is possible to keep the catalyst at a temperature of not less than its activation temperature for a long period of time even if the internal combustion engine stops.

By the way, when the internal combustion engine stops Just before a high-speed running of the hybrid vehicle, there is a possibility of reacting oxygen and fuel of non-combustion remained in the exhaust gas in the catalyst by increasing the temperature rise of the catalyst. This reaction greatly increases the temperature of the catalyst and thereby causes deterioration of the catalyst. According to the present invention, the pressure reducing means reduces the pressure in the accommodation space formed in the exhaust gas passage between the upstream-side and downstream-side throttle units, in which the catalyst unit with the catalyst such as a three way catalyst is placed. This decreases the amount of oxygen and uncombusted fuel in the exhaust gas around the catalyst. As a result, this limits the reaction of oxygen with the uncombusted fuel remained in the exhaust gas around the catalyst, and thereby prevents unnecessary temperature rise of the catalyst. It is thereby possible to prevent the deterioration of the catalyst while keeping the catalyst at the temperature of not less than its activation temperature.

The exhaust gas purifying apparatus as another aspect of the present invention further comprises a heating means capable of heating the exhaust gas remained in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle. The heating means heats the exhaust gas remained in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle. That is, the heating means heats the exhaust gas remained in the exhaust gas passage closed between the upstream-side throttle unit and the downstream-side throttle in which the catalyst is placed. Therefore the heating means heats both the catalyst and the exhaust gas remained in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle. It is thereby possible to stably keep the catalyst at the temperature of not less than its activation temperature for a long period of time.

The exhaust gas purifying apparatus as another aspect of the present invention further comprises a fuel injecting means, placed between the catalyst unit with the catalyst and the upstream-side throttle unit. This fuel injection means injects fuel into the inside of the exhaust gas passage which is positioned before the catalyst unit with the catalyst placed in the exhaust gas passage which is closed by the upstream-side throttle unit and the downstream-side throttle unit. The fuel injection means is placed at the upstream side observed from the catalyst unit with the catalyst. Injecting the fuel by the fuel injecting means performs the combustion of the fuel with oxygen remaining in the catalyst such as a three way catalyst. Adjusting the amount of the fuel to be injected by the fuel injecting means can keep the catalyst at the optimum temperature such as its activation temperature without excessive increasing of the catalyst temperature. It is thereby possible to prevent the deterioration of the catalyst while keeping the catalyst at the temperature of not less than its activation temperature for a long period of time.

The exhaust gas purifying apparatus as another aspect of the present invention further comprises a control means capable of instructing the upstream-side throttle unit and the downstream-side throttle to close the exhaust gas passage when detecting the stop of the internal combustion engine. When detecting the stop of the internal combustion engine, the control means instructs the upstream-side throttle unit and the downstream-side throttle to completely close the accommodating space in the exhaust gas passage. Accordingly, even if the amount of the exhaust gas flowing into the exhaust gas passage after the internal combustion engine stops, the control means limits the exhaust gas flow around the catalyst in the exhaust gas passage, and as a result, the temperature of the catalyst is kept at the optimum temperature. It is thereby possible to keep the catalyst at its activation temperature for a long period of time. Still further, the control means does not instruct the upstream-side throttle unit and the downstream-side throttle to close the exhaust gas passage while the internal combustion engine operates. It is thereby possible to decrease the pressure loss of the exhaust gas in the exhaust gas passage.

While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention which is to be given the full breadth of the following claims and all equivalent thereof. 

1. An exhaust gas purifying apparatus, to be mounted to a hybrid vehicle equipped with an internal combustion engine and an electric motor as power sources, capable of purifying an exhaust gas emitted from the internal combustion engine, the exhaust gas purifying apparatus comprising: an exhaust gas pipe that forms an exhaust gas passage through which an exhaust gas emitted from the internal combustion engine flows; a catalyst unit with catalyst placed in the exhaust gas passage; and a pair of an upstream-side throttle unit and a downstream-side throttle unit, placed at an upstream side and a downstream side observed from the catalyst unit along the exhaust gas passage, respectively, capable of opening and closing the exhaust gas passage.
 2. The exhaust gas purifying apparatus according to claim 1, wherein the throttle units completely close the exhaust gas passage in which the catalyst unit with the catalyst is placed.
 3. The exhaust gas purifying apparatus according to claim 2, further comprising a pressure reducing means capable of decreasing a pressure in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle.
 4. The exhaust gas purifying apparatus according to claim 2, further comprising a heating means capable of heating the exhaust gas remained in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle.
 5. The exhaust gas purifying apparatus according to claim 2, further comprising a fuel injecting means, placed between the catalyst unit with the catalyst and the upstream-side throttle unit, capable of injecting fuel into the inside of the exhaust gas passage positioned before the catalyst unit placed in the exhaust gas passage closed by the upstream-side throttle unit and the downstream-side throttle unit.
 6. The exhaust gas purifying apparatus according to claim 1, further comprising a control means capable of instructing the upstream-side throttle unit and the downstream-side throttle to close the exhaust gas passage when detecting the stop of the internal combustion engine.
 7. The exhaust gas purifying apparatus according to claim 2, further comprising a control means capable of instructing the upstream-side throttle unit and the downstream-side throttle to close the exhaust gas passage when detecting the stop of the internal combustion engine.
 8. The exhaust gas purifying apparatus according to claim 6, wherein the control means is an electronic control unit composed of a microcomputer that comprises a central control unit, a read only memory, and a random access memory.
 9. The exhaust gas purifying apparatus according to claim 1, wherein the catalyst is a three way catalyst placed in the catalyst unit. 